The objectives of this investigation are to determine the structural organization of the extracellular matrix and to establish the nature and mode of interactions between cells and the extracellular matrix and its specific components. Model systems consisting of fibroblasts and hepatocytes in culture will be examined, with particular emphasis on studies of the "substrate attached material" (SAM) produced by cultured fibroblasts. The organization of SAM will be investigated with morphological, biochemical and immunological techniques to determine the topographical interrelationships between its known components, i.e. fibronectin, collagen, heparan sulfate and hyaluronic acid. Further, the molecular structure and immunological properties of certain SAM components will be investigated, particularly the protein core of heparan sulfate proteoglycan. A major focus of this project will be the functions of SAM components and their interactions with cell surfaces. The structural basis for fibronectin-mediated cell adhesion and cell spreading will be investigated, and attempts will be made to isolate and characterize the "active sites" of the protein by limited proteolysis. Evidence will be sought for binding of fibronectin to cells, and membrane receptors will be isolated and characterized. Similar studies will be carried out to determine what structures in collagen are responsible for collagen-mediated cell adhesion and cell spreading. With the ultimate goal of defining more precisely the function of cell surface heparan sulfate, the binding of this glycosaminoglycan to cell membranes will be studied. Structural features of the polysaccharide which are required for the interaction will be determined and, subsequently, the corresponding receptors will be isolated and characterized. It is anticipated that this approach will yield important information concerning the normal physiology of the connective tissues and the changes which occur in joints, blood vessels and other locations in the course of rheumatic and cardiovascular diseases including diabetic vascular complications.